The present invention relates to a wiper pivot unit of a vehicle wiper.
Wipers for wiping windshield glass of vehicles are generally provided with pivot shafts having wiper arms attached to their tips, respectively. Each pivot shaft is rotatably supported by a pivot holder, which is fixed to a vehicle body, and the tip of the pivot shaft protrudes outward from the vehicle body. A pivot lever is fixed at one end to the proximal end of the pivot shaft, and a link rod is connected to the other end of the pivot lever. The link rod converts the rotary movement of a wiper motor into a swinging motion. The swinging motion of the link rod is reconverted by the pivot lever into rotary motion on the pivot shaft. The rotation of the pivot shaft pivotally reciprocates the wiper arm together with a wiper blade in a predetermined range, and the wiper blade wipes raindrops, mud and so on from the surface of the windshield glass.
However, in the conventional wiper, the pivot shaft protrudes outward from the surface of the vehicle body so that a wiper arm can be attached to the distal end of the pivot shaft. Therefore, the pivot shaft is susceptible to external impacts and loads. An impact or a load applied to the pivot shaft can damage the wiper itself and the periphery thereof.
In order to prevent such damage, Japanese Unexamined Patent Publication No. Hei 11-139256 discloses a wiper. In this wiper, a pivot shaft retracts into the vehicle body when it is subjected to a load exerted from the outside of the vehicle and absorbs the load.
More specifically, in this wiper, a constriction or an annular groove is formed at the middle part of the pivot shaft. A C-ring (a severed ring) is fitted to the annular groove. In the normal service condition, abutment of the distal end face of the pivot holder against the C-ring prevents axial movement of the pivot shaft with respect to the pivot holder.
The annular groove has a tapered side wall. When a load is applied to the wiper along the pivot shaft from the outside of a vehicle, the C-ring is expanded by the tapered side wall and escapes from the annular groove. Thus, axial movement of the pivot shaft is no longer prevented, and the pivot shaft retracts into the vehicle body to absorb the impact load.
However, in this wiper, a C-ring that has slipped out of the annular groove constricts the pivot shaft strongly, so that the pivot shaft resists being moved axially. In addition, the level of this resistance is not constant.
Accordingly, even if the axial movement of the pivot shaft is not presented by the C-ring, axial movement of the pivot shaft is restricted by the unstable and great resistance and by the reactive forces of the movement of the link rod connected to the pivot shaft through a lever fixed thereto and of a wiper motor. Also, there is a design problem in that it is difficult to set a threshold load for permitting axial movement of the pivot shaft.